In the LTE and LTE-A standards, the TDD system frame consists of ten subframes. 3GPP supports a total of seven kinds of frame structures, and Table 1 shows the uplink and downlink frame structures in the TDD system.
TABLE 1Uplink andDownlink-downlinkto-Uplinkstructureswitchingserialpointsubframe numbernumbercycle012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
Currently, the system information SIB-I is used in the 3GPP standard to notify the UE of the frame structure configured by the current serving cell. According to the existing standard, the minimum change cycle of the SIB information is 640 ms. The pre-research project “Dynamic TDD frame structure” formally approved in 3GPP RAN54 (December 2011) Plenary Session makes allocating the frame structures in the TDD system more dynamically possible. Shortening the change cycle of the frame structures in the TDD system can take full advantage of the TDD characteristics to better support the transmission of the asymmetric traffic.
At present, the uplink frame structure and downlink frame structure commonly used among the evolved NodeBs (eNB) are the same to avoid interference between the uplink and downlink of the eNB, however, since the information interaction between the eNBs takes a relatively long time, if the 10 ms-dynamic frame structure switch is applied, since there is not enough time for the eNBs to perform information interaction, it will bring the problem of the mutual interference of uplink and downlink between the eNBs.